The need for enhancing heat dissipation from some electronic components is well appreciated. Various electronic components, typically semiconductor devices, generate sufficient heat to adversely affect the operation thereof, if adequate heat dissipation is not provided. For example, power transistors and high performance CPUs typically generate enough heat to cause permanent damage to themselves.
According to contemporary methodology, the typical solution to such heat dissipation problems is to provide an external heat dissipator or heat sink to the electronic device. Such a heat sink ideally provides a heat-conductive path away from the electronic component to fins or other protuberances having sufficient surface area to dissipate the heat to the surrounding air. A fan is frequently used to assure adequate air circulation over the protuberances, so as to maintain desirable heat dissipation therefrom.
However, a common problem is that the surfaces of the electronic component and the heat sink, at the interface thereof, tend to be sufficiently irregular as to impede heat flow across the interface. The irregularity of the surfaces of the electronic component and heat sink at the interface thereof create air gaps or voids which reduce heat flow across the interface. As those skilled in the art will appreciate, heat flow across the interface improves substantially with better mechanical contact between the electronic component and the heat sink.
Although it is possible to machine the surfaces of the electronic component and heat sink at the interface thereof in order to improve the mechanical contact therebetween, it has been found to be prohibitively expensive to do so. Alternatively, contemporary methodology dictates that a viscous, heat conductive compound, typically silicone grease, be applied at the interface of the electronic component and the heat sink so as to fill voids formed therein. Thus, a substantially more complete and efficient heat path is provided from the electronic component to the heat sink.
However, as those skilled in the art will appreciate, the use of a silicone grease has inherent disadvantages. Silicone grease is inherently messy and tends to soil personnel, clothing, and equipment, as well as nearby electronic components. Silicone grease is difficult to effectively clean, particularly from electronic assemblies.
Further, such use of silicone grease entails properly metering and applying the same to the desired electronic components and/or heat sinks in order to be effectively and economically utilized. The metering and application of silicone grease is inherently difficult and time consuming. Costly machinery is required to automate the process.
Further, silicone based thermal greases inherently migrate, over time, away from surfaces upon which they are initially applied. This migration of silicone based thermal greases facilitates the formation of air gaps or voids at the thermal interface. As those skilled in the art will appreciate, such air gaps or voids substantially reduce heat transfer across the thermal interface.
In an attempt to overcome the well known deficiencies of silicone grease, various heat conductive pads have been developed. Such heat conductive pads are typically preformed to have a shape or footprint compatible with a particular electronic component and/or heat sink, such that they may easily be applied thereto prior to attaching the heat sink to the electronic component.
Two examples of such contemporary pad-type thermal interfaces are THERMSTRATE and ISOSTRATE (both registered trademarks of Power Devices, Inc. of Laguna Hills, Calif.).
The THERMSTRATE interface comprises thermally conductive, die-cut pads which are placed intermediate the electronic component and heat sink so as to enhance heat conduction therebetween. The THERMSTRATE heat pads comprise a durable, type 1100 aluminum alloy substrate having a thickness of 0.002 inch and are coated on both sides with a proprietary thermal compound. The thermal compound comprises a paraffin base containing additives which enhance the thermal conductivity thereof. Additives also control the response of the thermal compound to heat and pressure. THERMSTRATE is dry on assembly, i.e., at room temperature, yet provides excellent wetting at the operating temperature of the electronic component to which it is applied, so as to assure desired heat conduction.
The ISOSTRATE thermal interface is likewise a die-cut mounting pad and utilizes a heat conducting polyamide substrate, i.e., KAPTON (a registered trademark of DuPont) Type MT. The ISOSTRATE thermal interface likewise has a propriety paraffin based thermal compound utilizing additives to enhance thermal conductivity and to control its response to heat and pressure.
Both THERMSTRATE and ISOSTRATE thermally conductive heat pads are silicone free and provide a no-mess, no-waste permanent replacement for thermal grease and the like. Such thermally conductive pads eliminate the problems and expense of handling and soiling which are commonly associated with the use of silicone grease.
The process for forming thermal interfaces according to contemporary methodology is described in more detail in U.S. Pat. No. 4,299,715 issued on Nov. 10, 1981 to Whitfield, et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; U.S. Pat. No. 4,466,483 issued on Aug. 21, 1984 to Whitfield, et al. and entitled METHODS AND MEANS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE; and U.S. Pat. No. 4,473,113 issued on Sep. 25, 1984 to Whitfield, et al. and entitled METHODS AND MATERIALS FOR CONDUCTING HEAT FROM ELECTRONIC COMPONENTS AND THE LIKE, the contents of all three of which are hereby incorporated by reference.
However, to date, no pad thermal interface is known which provides adequate heat dissipation, is inexpensive to manufacture, and which utilizes an adhesive to attach the pad to either the electronic component or the heat sink.
The prior art practice of adhesively bonding the thermal interface to either the electronic component or the heat sink is well known. Such practice facilitates handling of the interface and also allows the heat conductive interface to be sold along with either the electronic component or the heat sink already in place thereon.
Generally, according to contemporary practice, the use of an adhesive material to attach the heat conductive interface to either the electronic component or the heat sink is thought to be undesirable. It is thought that the addition of such an adhesive layer to the interface would undesirably reduce heat conduction from the electronic component to the heat sink. This is particularly true since, according to contemporary methodology, the addition of an adhesive layer entails the addition of a substrate and the addition of a second adhesive layer.
For example, one prior art attempt to utilize adhesive to attach a pad thermal interface to either an electronic component or heat sink involves the fabrication of a pad having six layers, as discussed in detail below. As those skilled in the art will appreciate, heat flow is substantially reduced by such additional layers.
Not only does each individual layer impede heat flow, but, as those skilled in the art will appreciate, each interface of different adjacent layers additionally inhibits heat flow. Thus, each layer contributes three distinct impediments to heat flow. It introduces the material of which the layer itself is comprised, as well as the two interfaces at either surface of the layer. Thus, it will be appreciated that it is highly desirable to minimize the number of layers, and consequently the number of interfaces.
It has been found that the use of a thermal interface having six layers does not provide desirable heat transfer from the electronic component to the heat sink. Such a six layer pad is also expensive to manufacture. Thus, it is desirable to minimize the number of layers defining the thermal interface.
As is typical for attaching a heat sink to an electronic component, clips, clamps, fasteners, or other devices may be utilized so as to further assure adequate contact of the heat sink and electronic device at the interface thereof, and also so as to assure that the heat sink remains reliably attached to the electronic component. This is of particular concern since different adhesives have different curing rates and bonding strengths.
As such, it is beneficial to provide a thermal interface pad which is adhesively bondable to either the electronic component or the heat sink, which does not substantially reduce heat flow from the electronic component to the heat sink, and which does not substantially increase the manufacturing cost thereof as compared to contemporary thermal interfaces pads.